This invention relates to a retractable mechanism for a writing element.
In well known writing instruments of the ball point type, the writing element comprises a refill which contains the writing fluid and has a writing tip of known ball point construction. Where the writing element is desired to be retractable between an extended position in which the writing tip is projected out of a housing for writing purposes and a retracted position in which the writing tip is retracted wholly within the housing for avoiding the inadvertent transfer of writing fluid, a retractable mechanism is provided.
More especially this invention relates to a retractable mechanism for a writing element comprising a plunger, passage means defining a passage in which said plunger is constrained to move in the longitudinal direction of said passage, a pair of latch means oppositely disposed when viewed in a plane normal to said longitudinal direction, a latch member reciprocally displaceable in said longitudinal direction by means of said plunger, said latch member having a pair of laterally extending latch arms oppositely directed and each disposed for engagement with a respective one of said latch means, one of the latch means defining a forward, projected position of the writing element and the other of the latch means defining a rearward, retracted position of the writing element, when present the writing element is resiliently biased to urge the latch member rearwardly in its longitudinal direction to ensure that one of said abutment means engages with its associated latch means, advance of the plunger in the forward longitudinal direction releasing the engaged one of the abutment means from its latch means whereby the latch member may be displaced laterally to ensure alignment of the other of said abutment means with its associated latch means thereafter to engage therewith whereby the writing element may be displaced between its retracted and projected positions (or vice versa) in response to successive depressions of the plunger. Such a retractable mechanism is referred to herein as a retractable mechanism as hereinbefore defined.
One prior art retractable mechanism disclosed in United Kingdom Pat. No. 804,903 has the features of the retractable mechanism hereinbefore defined. The plunger has a pair of strike faces which alternately on successive depressions of the plunger strike respective ones of two cam faces on the latch member. The latch member has a rearward limb which at its rearward end defines the pair of cam faces individually associated with the plunger strike faces. The rearward limb of the latch member has a pair of latch rockers, or pivots, each of which is a pivot for a fulcrum action of the latch member thereabout when in contact with a respective interior wall portion of the passage. These latch rockers and the cam faces are located on opposite sides of a longitudinal centre line through the rearward limb of the latch member. The rearward limb extends from a base of the latch member having a planar forward bearing surface which seats on an adaptor cap fitted on the rearward end of the writing element and also carries the laterally extending oppostely directed abutment means, which are termed latch arms in that patent. Also in that patent the latch means are termed latch shoulders. In the operation of this prior art retractable mechanism, assuming the mechanism is assembled and operational, one of the latch arms will be in engagement with its respective latch shoulder (say the rearward latch shoulder defining the retracted position of the writing element). With the writing element retracted, the cam face on the side of the latch member remote from the engaged latch arm should be positioned such that, as the plunger is depressed, a respective one of the plunger strike faces strikes that cam face to advance the latch member longitudinally in the passage. This action maintains the latch rocker (or pivot), on the same side of the latch member as the engaged latch arm, in contact with the interior wall of the passage and, as the latch member advances sufficiently to release the engagement between the latch arm and the rearward latch shoulder, the force of the plunger strike face acting on the cam face causes the latch member to pivot about the latch rocker and displace the other latch arm laterally towards the forward latch shoulder which it engages when the plunger advances latch member forwardly below the forward latch shoulder. When the plunger is released, the resilient bias acting on the writing element causes the latch member to pivot at the point of engagement between the latch arm and the forward latch shoulder to bring the other latch rocker into contact with the interior wall of the passage adjacent thereto and thereby align the other cam face (the one nearest to the latch arm engaged with the forward latch shoulder) for contact by its associated plunger strike face on the next depression of the plunger. The next depression of the plunger similarly releases the now engaged latch arm from the forward latch shoulder, and the force of the strike face on the cam face effects pivoting of the latch member about the latch rocker in contact with the passage interior wall resulting in lateral alignment of the other latch arm with the rearward latch shoulder. Thus, the rearward latch shoulder is engaged by its associated latch arm when the plunger is released and the latch member moves rearwardly due to the resilient bias acting on the writing element. After this engagement, the other latch rocker (or pivot) is brought similarly into engagement with the passage interior wall adjacent thereto such that the cam face on the latch member required for the next depression of the plunger is aligned for contact by its respective strike face.
In U.K. Pat. No. 804,903, the correct alignment of the cam faces on the latch member for contact of the required one of them by its associated plunger strike face when the plunger is next depressed is critical to the operation of this retractable mechanism. Likewise, the location of the latch rockers or pivots on the sides of the latch member rearward limb is critical. Furthermore, a high degree of precision of alignment in the assembly of the components is critical to reliable operation of this retractable mechanism. The embodiment illustrated in the patent requires a multiplicity of components which can lead to high material costs, high production labour costs and the problem of high failure rates in an automated assembly situation.